We are continuing our studies on the isolation and properties of the inhibitory protein as well as on the nature of the modification of RNA polymerase elicited by infection with T3 phage. During the course of these studies we have purified a novel polyriboadenylate polymerase to near homogenity which can utilize either ATP or ADP as substrate. This enzyme is distinct from polynucleotide phosphorylase and can form poly(a) in the absence of a primer. Based on the 32p exchange studies, we have been able to advance a mechanism for the enzymatic reaction. These new developments have also led us to the identification of poly (A) stretches in bacterial pulse labeled RNA. The addition of poly (A) to RNA appears to be post-transcriptional. Our initial studies have shown that T7 early messenger RNA does not contain poly (A). BIBLIOGRAPHIC REFERENCE: "Presence of Polyriboadenylate Sequences in Pulse-labeled RNA of Escherichia Coli." P.R. Srinivasan, M. Ramanarayanan, and Elazar Rabbani. Proc. Nat. Acad, Sci. USA 72, 2910, 1975.